Conjugation reactions with an endogenous substrate, Glucuronic acid, Sulphuric acid, Acetic acid, amino acid, if the phase I metabolite is too lipophilic.
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What is the most important/common conjugation reaction?
Glucuronidation
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If the compound has..., .... or ... it enters phase II directly
-OH, -NH2, -COOH
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Write the glucuronidation reaction.
Drug + UDP-glucuronic acid --(UGT enzyme)--> Drug-glucuronide conjugate
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What is the effect of enzyme inhibition?
Decrease in the metabolism of substrate and so increases drug exposure.
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What is the effect of enzyme induction?
Increased gene transcription, metabolism increases, drug exposure decreases. Take a few days for full effect
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Glomerular filtration: rate of entry is dependant on...
1) Concentration of free drug in plasma 2) Mr
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Tubular reabsorption: Name the three stages
1) Enters glomerular filtrate 2) Active secretion 3) Passive reabsorption if lipid soluble
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Tubular secretion: What are the two systems for?
Acids, bases
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What happens if the fluid becomes more alkaline?
The acidic drug ionises --> LESS lipid soluble and so reabsorption diminishes. The opposite is true for the basic drug.
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The extent of absorption is dependant on...
Drug lipid solubility (pKa) and pH of tubular fluid
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